Initially growing up seemed time of great enjoyment (5)
I believe the answer is:
gusto
'great enjoyment' is the definition.
(as in doing something with gusto)
'initially growing up seemed time of' is the wordplay.
'initially' says to take the initial letters.
The first letters of 'growing up seemed time of' is 'GUSTO'.
(Other definitions for gusto that I've seen before include "exhilaration" , "Relish; vigour" , "Exuberant enjoyment" , "Hearty enjoyment" , "Zest, pleasure in action" .)